In many parts of the world there is much fear among divers of attack by predators. The white-pointer shark in some waters has been known to take lives, and attacks have also been made by other species of shark including tiger sharks, the whaler species and mako sharks. Much valuable diving time is lost due to the prevalence of predators, and particularly due to risk of attack in turbid water and it is therefore desirable that the divers should have some means of protecting them against attack. A diver is considered most vulnerable to shark attack when at the surface.
Divers are also subject to "bends", a sickness which is caused by rapid decompression and excessive exertion. There is also a need to provide means whereby a diver can travel beneath the surface of the water for extended periods of time without the exertion required by swimming. Another factor which reduces the incidence of bends is the temperature and fatigue to which the diver is subject.
When abalone are gathered by normal means, bags are filled and brought to the surface by the diver. However it is desirable that the abalone diver should be able to remain beneath the surface for extended periods, and be able to send bags of abalone to the surface as soon as they are filled, thereby increasing the catch possible in a given period of time.